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Re: CONCRETE: Repair of Segmental Post-Tensioned Concrete Tank

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Bill,
 
Having some experience with tank design, my biggest concern would be the reinforcement that is likely damaged (possibly, beyond repair) by the long-time leaks. The subsequent loss of the hoop compression/post-tension may be one of the causes of the leaks. 
 
This means that simple religning and shotcreting is insufficient; most likely, new post-tensioned reinforcement is required. 
 
Is the existing concrete adequate for that? Even if it is, at the end of the day, it may be just cheaper to replace the tanks.
 
Both the deterioration and the possibility of failure are likely to be progressive.  Make sure you are on the record pointing to that. How big is the tank? 
 
Steve Gordin, SE
Irvine CA
----- Original Message -----
Sent: Thursday, July 28, 2005 9:49 AM
Subject: CONCRETE: Repair of Segmental Post-Tensioned Concrete Tank

Hi, folks.

I have a weird one here: A Post-Tensioned tank that was done back in the
70s or thereabouts. The weird thing about it is, that it we done using
essentially tilt-up panels with ducts cast into them horizontally, then
threaded together with PT cables that were then tightened and the
anchorages (such as they were) grouted into pockets occasionally occurring
in the panels.

Then, the joints between the panels were grouted.

As you might guess, those joints are the problem: Over the years they've
continually leaked. You can see where urethane injection has been employed
numerous times (the injection ports / packers are still in place with
dried urethane oozing out of them--it's really an ugly mess).

The contractor that provides the occasional injection reports that they
cannot get any more urethane in, it just "won't go" any more.

So now the client wants alternative methods of repair. I'm on record as
saying that I believe the tank must be replaced, that repair would be
costly (probably requiring, say, a rubberized or otherwise flexible tank
liner together with, say, a new shotcrete shell--possibly requiring some
repiping.

And even then I'm not sure that the thing would last indefinitely.

Anyway, are there other repair schemes available to anyone's knowledge?
One thing to keep in mind is that I'm pretty certain the existing tank
walls need to be discounted for strength. If they're not already pretty
much "shot," it's only a matter of a short time until at least one of the
panels will "go." It's kind of a scarey situation.

Anyway, I think the client's onsite management would be quite happy to
entertain notions of replacing the tank altogether.

Comments?

Thanks in advance.


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